Given the task definition and input, reply with output. In this task, you're given a context passage, followed by a question that needs to be answered. Based on the paragraph, you must write unambiguous answers to the questions and your answer must refer to a specific phrase from the paragraph. If multiple answers seem to exist, write the answer that is the most plausible.

On this day in 1846, Congress voted overwhelmingly to approve a declaration of war against Mexico sought by President James Polk. By the war's end in 1848, Mexico had lost nearly half its territory. 
Question: What does Taylor need to do before this?

Under the Treaty of Guadalupe Hidalgo, the Rio Grande became the southern boundary of Texas